Any device that intentionally uses, but does not intentionally radiate RF energy, is classified by the FCC as an Unintentional Radiator and it is subject to technical and administrative requirements in Section15, Subpart B.

A device that produces RF energy only as a by-product of its operation (e.g., a motor) is classified as an Incidental Radiator and is subject to the general requirements in Sections 15.5 & 15.13.

A device that incorporates a switching power supply is clearly a digital device since it intentionally uses a switching regulator operating over 9 KHz to convert electrical power efficiently and is considered a sub-class of Unintentional Radiators.

A device that incorporates a Linear Amplifier may be an Incidental Radiator, provided there are no RF generating components in the device.